This application relates to and incorporates herein by reference Japanese Patent Application No.11-68865 filed on Mar. 15, 1999.
1. Field of the Invention
The present invention relates to load detection sensor units for beddings, and particularly to a load detection sensor unit for use on an air mat.
2. Related Art
JP-A-2-41158 discloses an air mat which is comprised of a plurality of air cells. The pressure of the air cells is varied at regular time intervals to restrict bedsores of sleepers such as aged persons or sick persons lying on the air mat for months. The pressure is varied uniformly in all the air cells. Therefore, this air mat cannot restrict the bedsores from growing.
It is proposed to use a load detection sensor unit comprising a plurality of load detection devices, so that a posture of a sleeper is determined based on output signals of the detection devices. It is however impractical to extend signal output lines from the detection devices to a signal processing circuit external from the load detection sensor unit.
If the load detection sensor unit is used on the air mat of the above type, it must be constructed with an elastic film to change its shape with changes in the shape of air cells. Further, if an electrical circuit of the signal processing circuit which is generally rigid is integrated with the load detection devices, electrical connections between the elastic film and the electrical circuit must be ensured.
It is therefore an object of the present invention to provide a load detection sensor unit which requires less electrical signal lines for connection with an external electrical unit.
It is another object of the present invention to provide a load detection sensor unit which ensures good electrical connections between load detection devices made of an elastic film and an electrical circuit integrated with load detection devices.
According to the present invention, a load detection sensor unit for a bedding includes a plurality of load detection devices arranged as a part of the bedding for producing output signals variable with load applied thereto by a sleeper, respectively, and switches for turning on and off a transmission of the output signals of the detection devices to the signal line. The switches are turned on sequentially to serialize the output signals of the detection devices to be transmitted serially to an external electrical unit through a single signal line.
Preferably, the load detection devices are formed integrally with a signal processing circuit including the switches and the single signal line on an elastic film. The load detection devices and the signal processing circuit are electrically connected to each other through elastic conductors.